(a) Field of the Invention
The present invention relates to a power train of an automatic transmission. More particularly, the present invention relates to a power train of an automatic transmission with eight forward speeds and two reverse speeds.
(b) Description of the Related Art
A typical shift mechanism of an automatic transmission utilizes a combination of planetary gear sets. A power train of such an automatic transmission changes rotating speed and torque received from a torque converter of the automatic transmission, and accordingly changes and transmits the changed torque to an output shaft.
When a transmission utilizes a relatively large number of shift speeds, speed ratios of the transmission can be optimally designed, and therefore a vehicle can have better fuel mileage and better performance than those with fewer shift speeds.
In addition, features of a power train such as durability, efficiency in power transmission, and size depend a lot on the layout of combined planetary gear sets.
A manual transmission with many speeds causes the inconvenience of excessively frequent shifting operations by the driver. Therefore, transmissions with large numbers of shift-speeds lend themselves to automatic transmissions.
In addition, as more speeds are utilized, a power train that can easily skip up-shift and skip down-shift as well as normally up-shift and down-shift is required.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.